There currently exist no effective pharmacological treatment options to prevent relapse to cocaine and heroin seeking. This is due to a principal lack of understanding of the underlying maladaptive cellular mechanisms driving this behavior. Considerable evidence suggests that the pre-frontal cortex (PFC) projection to the nucleus accumbens core (NAcore) represents a principle common pathway for triggering relapse. Recently, we found in rats that cocaine or heroin SA induces persistent hyper-excitability in PFC pyramidal neurons. The hyperexcitability is related to elevated intracellular Ca2+ that likely arises from malfunctioning ryanodine receptors (RYRs). Excess Ca2+ suppresses inhibitory Kv7 ion channels that serve to limit neuronal firing. Notably, this drug-induced malfunction in cell signaling persists even after extended extinction of the drug- reinforced behavior. As a result, a subpopulation of PFC neurons remains hyper-excitable and likely hypersensitive to drug-associated cues. In hippocampal neurons, excessive stimulation by stress is associated with phosphorylation and oxidation of RYR2 and depletion of the stabilizing subunit calstabin2 (FKBP12.6) from the channel complex, resulting in intracellular Ca2+ leak through RYRs and cognitive dysfunction. A novel RYR-targeted small molecule Rycal (S107) that stabilizes the RYR2 closed states of PKA hyperphosphorylated, and oxidized/nitrosylated channels, prevents intracellular Ca2+leak and prevented the stress-induced cognitive defects. Our preliminary data indicate that S107 treatment also reduces cue-induced cocaine seeking in rats. The long-term goal of this project is to understand the cellular signaling and physiological mechanisms by which RYRs regulate relapse behavior in hopes of identifying better therapeutic strategies for the treatment of drug addiction. Our central hypotheses are that: (1) cocaine- and heroin- produces pathological destabilization of RYR via redox post-translational modification, 2) causing RYR- dependent Ca2+ leak within activated PFC neurons projecting to the nucleus accumbens core (NAcore), and 3) that the anti-relapse effects of the RYR stabilizer S107 are due, at least in part, to its ability to reduce RYR Ca2+ ?leak?. To better understand the cellular origin of the enduring adaptations in PFC inhibition, we propose to examine: the redox state of RYR and a battery of biochemical changes in both RYR and FKBP12.6 in Aim 1, RYR changes in specific subpopulations of neurons in Aim 2, and lastly translational strategies aimed at reducing cued reinstatement of drug seeking in Aim 3. Together, these studies will extend our extensive preliminary findings that link the RYR redox state and the candidate addiction therapeutic, S107 to regulation of relapse-like behaviors that drive the long-lasting changes observed in the PFC. We will determine if disruption of the PFC RYR2 and/or FKBP12.6 by cocaine and heroin is necessary for relapse and will provide mechanistic preclinical data in support of a novel target for drug development to treat heroin and cocaine addiction.